Waste liquids such as metal plating waste liquids and waste liquids from cleaning printed-circuit boards contain organic substances including, for example, higher alcohols, sulfide compounds, alkylthiosulfate compounds, nitrogen-containing alkyl compounds, phosphoric acid compounds, and the like in large amounts. Conventionally, the organic substance-containing waste liquid has been treated by, for example, subjecting an organic substance-containing waste liquid to steam-heating, thereby separating water as distilled water (see, for example, Japanese Patent Laid-Open No. 2003-89899); subjecting the organic substance-containing waste liquid to an electrolytic oxidation treatment or to a precipitation-and-collection treatment in the presence of chlorine ions (see, for example, Japanese Patent Laid-Open No. 2005-76103); subjecting the organic substance-containing waste liquid to frozen concentration to remove insoluble components (see, for example, Japanese Patent Laid-Open No. 2003-164862); or the like.
On the other hand, an organic substance-containing waste liquid such as a waste water from a food processing factory, a domestic waste water, or a raw sewage, has been treated according to an activated sludge method. However, when the activated sludge method is applied to the treatment of an organic substance-containing waste liquid such as a metal plating waste liquid or a waste liquid from cleaning a printed-circuit board, there are some disadvantages such as the removal of a substance affecting a BOD value or the like, the degradation removal of a sulfur-containing compound, and the removal ratios of a total nitrogen and a total phosphorus are low, so that the organic substance-containing waste liquid often produces foams or becomes turbid, thereby making it difficult to perform the treatment of the waste liquid. In addition, when the activated sludge method is applied to the treatment of an organic substance-containing waste liquid such as the metal plating waste liquid or the waste liquid from cleaning printed-circuit boards, there is a disadvantage that a foul odor may be generated in some cases.
In addition, scum is often generated in the process or equipment for treatment of a waste water, such as sewage treatment or domestic waste water treatment, and further experimental waste water treatment, factory waste water treatment, livestock waste water treatment, or sludge treatment, and is considered as a disadvantage as a great phenomenon of inhibiting normal operation of waste water of the process and equipment for treatment of a waste water. The scum is generated upon change of seasons (October to November and April to June in Japan), or when fluctuations of BOD loads are in extreme, i.e. when the load is light or excessive, or when BOD of a raw sewage is extremely high, or when a sludge concentration is extremely high, or upon fluctuations of pHs of a raw sewage, upon inflow of the sludge, upon lowering of a water temperature, or the like. In an earlier stage of generation of the scum, the sludge is suspended and separates from an aqueous phase to be suspended to cover the entire aeration tank, and the sludge flows into a precipitation tank and thus undesirably flows into a drainageway in the state of being incapable of providing liquid-solid separation. Also, since the liquid-solid separation can be prevented in the precipitation tank of the waste water treatment equipment, the quality of the treated water is drastically worsened. In addition, when the generated scum is allowed to stand, the activated sludge in the treatment tank forms scum, and the scum is in turn suspended, so that the contact of the foul water and the activated sludge is prevented, thereby impeding aeration efficiency, causing lowering of the treatment efficiency and causing treatment hindrance, and at the same time generating foul odor.
The above-mentioned generation of scum in an early state is also referred to as bulking, which is referred to those (1) in the state in which sedimentation of the sludge is controlled by the action of a filamentous fungus of the genus Sphaerotilis; (2) in the state in which bubbles that are less likely to be broken by aeration are formed (so-called foaming phenomenon), and sludge is adsorbed to the bubbles to be suspended, and the sludge is separated to form a layer on the surface of the aeration tank to be suspended (see The Microbiology of Activated Sludge, eds. R. J. Seviour et al., Kluwer Academic Publishers, Rordrecht, Netherlands, 1999, pp. 99-121, 147-202); and further (3) in the state where sludge is no longer suspended in water in the aeration tank, the sludge concentration tank or the precipitation tank even without the foaming phenomenon, so that the sludge is separated to be suspended; and the like.
In view of the above, the development of a method of controlling the generation of the scum, foaming or bulking, or eliminating the generated scum, foams or bulking in a very short period of time has been earnestly desired. For example, there is a method in which sedimentation property of the sludge is improved and the treatment efficiency of the activated sludge is improved, whereby consequently controlling the generation of scum (see Japanese Patent Laid-Open No. Hei 6-170387). When the scum is generated, the scum treatment is improved by adding alanine, magnesium sulfate, soluble silicic acid, or a silicate in a large amount against displacement to be treated; however, it has been reported that when a water temperature is elevated, the elimination of scum is not sufficient even with the treatment (Ryozo and Hideki (1999) Journal of Antibacterial and Antifungal Agents, Japan) 27(7): 431-440). As described in the same journal, a decisive solution strategy that can always be taken for the generation of scum, foaming or bulking against an operation at a low temperature, an operation at a high temperature, or an abnormal condition of treated water has not yet been found at present.